1. Field of the Invention
The present invention relates to the technology concerning Internet Protocol version 6 (IPv6) and, more particularly, to a mobile node, a mobility control apparatus, a communication control method, a communication system, and a data format.
2. Related Background Art
In the Internet through Internet Protocol version 6 (IPv6) (for example, reference is made to “S. Deering and R. Hinden, “Internet Protocol, Version 6 (IPv6) Specification”, Request For Comments 2460, December, 1998”), Mobile IPv6 (e.g., reference is made to “C. Perkins and D. B. Johnson, “Mobility Support in IPv6”, draft-ietf-mobileip-ipv6-18.txt, June, 2002”) is presented as a conventional technique enabling a node to maintain communication with a correspondent node even if it successively changes connected links with movement. Mobile IPv6 provides definitions of Mobile Node (MN) which is a node moving on the Internet, and Home Agent (HA) which exists on a predetermined link of Internet and which forwards a packet addressed to MN, to MN. MN uses a Home Address (HoA) determined from a link on which HA used by itself exists, and a Care-of Address (CoA) determined from a link on which MN itself exists at present. MN updates the CoA to another upon every migration. Then MN sends a Binding Update (BU) message to HA to advertise HA of a binding indicating a correspondence between the HoA and the new CoA. HA puts a packet addressed to the HoA of MN, which was sent from a correspondent of MN, into a packet addressed to the new CoA indicated by the binding, and forwards it to the CoA. Mobile IPv6 guarantees communication between MN and the correspondent node by the above-described operation.
HA continues forwarding packets to the old CoA, before MN migrates to switch its link connected to the Internet and then update the CoA to the new and before HA updates the binding of MN under its management. After completion of the binding update process, HA starts forwarding packets to the new CoA. Since packets having been forwarded to the old CoA are forwarded to the link used for connection before the migration by MN, they are not received by MN to end in burst packet loss.
In order to decrease the duration of the binding update process leading to the burst packet loss, there is a proposal to implement Hierarchical Mobile IPv6 adopting Mobility Anchor Point (MAP) between HA and MN (e.g., reference is made to “H. Soliman, et al., “Hierarchical MIPv6 mobility management (HMIPv6)”, draft-ietf-mobileip-hmipv6-06.txt, July, 2002”). In Hierarchical Mobile IPv6, HA manages the binding between HoA and MAP address, and MAP the binding between HoA and CoA. When MN switches its connected link in an identical MAP domain, there is no need for updating the binding managed by HA and it is sufficient to updating only the binding managed by MAP. Since a transmission delay between MN and MAP is smaller than that between MN and HA, the binding update duration with MAP becomes shorter than that with HA. Therefore, in switching the connected link in the same MAP domain, Hierarchical Mobile IPv6 can decrease the burst packet loss more than Mobile IP.